For years food scientists have had a continuing interest in producing palatable, nutritious proteinaceous food products from plant sources as a supplement to or as a replacement for animal protein foods. The proteinaceous products must be economical, nutritionally well balanced and aesthetically acceptable to the human consumer, i.e. the product must be bland in flavor and odor and must be free of objectionable colors. At the present time, such proteinaceous food products are principally prepared from soybeans. Unfortunately, the soy proteins are relatively deficient in some essential sulfur bearing amino acids.
It is well known that many of the inherent disadvantages of soybeans can be overcome by combining the soy protein with proteins from another source. For example, the protein from cereal grains has a good amino acid balance and high biological value. Thus, because of their low cost and nutritional value, the crude grain glutens from such cereals as corn, sorghum, wheat and the like have been frequently suggested as having potential use, in combination with soy protein, in food products. In particular, it has been suggested to use corn gluten. Major obstacles, however, to the general use of crude grain gluten have been the characteristic bad flavors and odors, intense colors, oils, and high moisture contents of these potential sources.
Considerable efforts have been made in the past to prepare protein products from grain gluten using classical methods, but such efforts have been only moderately successful. These efforts have not allowed the valuable protein to be recovered in commercial quantities at low cost or completely free of the gluten's characteristic flavors, odors, colors, carbohydrates or salts.
Generally, the classical methods of extraction using linear hydrocarbon solvents have not been satisfactory due to the immiscibility of the solvents with the high amounts of water usually present in the grain gluten. Hydrophilic solvents, such as the lower aliphatic alcohols, have also been used for deoiling oilseeds, but they cannot be used successfully with aqueous wet gluten without serious loss of the alcohol soluble protein fraction. Other solvents, as disclosed in Canadian Pat. No. 378,122, such as ethyl acetate, acetone, benzene, petroleum fractions, ether and the like have been used under moderate temperatures and high pressure conditions to retain enzyme activity and extract oils from dry beans and seeds, but the resulting product is substantially unchanged other than the decrease in oil content. Solvent mixtures, as disclosed in U.S. Pat. No. 3,408,374, such as ethanol-ethyl acetate-acetone (1:1:1) and ethanol-ethyl acetate-isopropyl ether (4:2:1) have likewise been used to extract aqueous wet, oil-bearing vegetable materials, but residual water soluble components still remain in the solvent extracted raw material. In each case, the prior art techniques are costly and the products which result are not completely satisfactory.